Larimer County develops hit list of top 10 weeds
By Ellen Nelson
Larimer County Weed District
Killing weeds is a never-ending battle these days, and it requires lots
of cooperation from landowners.
The following top-10 weed list is based on the number of landowner calls,
complaints and questions received by the Larimer County Weed District and
the district's concern about the weed's invasiveness and difficulty to
control.
Not all of these weeds are on the county noxious weed list. For example,
kochia is so prevalent and so opportunistic in colonizing any bare ground,
that it is a concern to many landowners. Others, such as the knapweeds,
are not only on the county noxious weed list but are increasing in Larimer
County. And the number one weed, leafy spurge, is on the county noxious
weed list, is very difficult to eradicate and is found throughout the county.
10. Kochia – An eager and energetic annual weed, it readily colonizes disturbed
sites, such as old corrals and abandoned agricultural fields. It is found
everywhere and, if left unchecked, can reach heights of 4 to 6 feet. Kochia
remains until a strong wind sends it tumbling across the landscape to scatter
seed and collect along fence lines in fall and winter.
9. Russian olive – This plant was originally welcomed to Larimer County
for windbreaks and erosion control. It is now a pariah. Easily spread by
birds, it can dominate riparian areas and crowd out native species such
as cottonwoods and willows.
8. Common mullein – A show-off with tall spiky candle-like flowers, this
weed produces thousands of seeds that remain viable for 80 years in the
soil. Because it is a biennial, pulling or digging the rosettes can be
effective control.
7. Cheatgrass – The grass everyone loves to hate, it provides a beautiful
flush of green in the spring. Mule deer are happily feeding on it now,
but it will soon dry out and become prickly awns on socks, dogs and livestock
as it spreads to new sites.
6. Musk thistle – With a large, showy purple thistle head on the end of
a stalk, this biennial reproduces from seed. Prevent new seeds from entering
the seed bank by pulling off that seed head, bagging and removing it.
5. Dalmatian toadflax – This showy ornamental plant was originally introduced
for landscaping, but adapted too well, escaped and went feral. This weed
is rapidly colonizing much of the foothills open land along the Front Range.
There is a stem-boring weevil available as an effective biocontrol.
4. Diffuse and spotted knapweed – These similar plants are often found
together. They produce lots of seed and can spread rapidly to take over
pastures and rangelands.
3. Russian knapweed – This weed is found in pastures and hay fields. If
a horse consumes too much, a fatal nervous disorder called "chewing disease"
can result.
2. Canada thistle – Because of deep roots, this plant is almost indestructible
and very difficult to control. It also reproduces by seeds, which remain
viable in the soil up to 20 years. Mowing may decrease seed production,
but unless a landowner kills the roots, it will continue to increase and
crowd out desirable native grasses.
1. Leafy spurge – Thirty-five years ago, leafy spurge was a newcomer to
Larimer County. Now it "owns" large tracts of land here. Those who do not
want this weed to take over their land should contact the Larimer County
Weed District at 498-5768 or http://www.larimer.org/weeds/ for free help
identifying plants and developing land management plans
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